Gas lift control system



June 29, 1965 L. M. HUBBY eAs LIFT coNTRoL SYSTEM Filed Sept. 6, 1962United States Patent O 3,191,681 GAS LIFT CNTRL SYSTEM Laurence M.Hubby, Bellaire, Tex., assignor to Texaco Inc., New York, N.Y., acorporation of Delaware Filed Sept. 6, 1962, Ser. No. 221,790 6 Claims.(Cl. 16652) This invention is concerned with oil iields generally andmore specifically concerns a system for use in a producing oil fieldthat is being produced by the so-called gas lift type of well iluidrecovery.

Heretofore in most gas lift operations each Well in a iield isindividually controlled, as to the `on-off cycles of its gas liftoperation, by use lof `a spring driven clock mechanism. Under sucharrangement, the clocks employed cannot be synchronized and consequentlyno matter how accurate they are they all run at lslightly differentspeeds. lFor this reason although the operating cycle of each well maybe originally set so .as to stagger the on time for all of the wells inthe lield to provide sequential operation, :after some time thestaggered sequence will be gradually lost -by reason of the differentspeeds involved in the spring Wound time controls. Thus at various timesthere will be several of the wells having the on portion -of the cycleoccur simultaneously, and this will cause overloading of the power gassupply system and in the ilow of production fluid to the tank batterysince the most economical :arrangement is to provide ilow capacity onlysuflicient to take care of the ilow from each well separately. Theindicated overloading will cause various problems, such as a higher backpressure on the llow lines which results in lower elliciency of the gaslift operation.

By employing -a system according to this invention, the actu-ation ofindividual well gas lift cycles may be centrally controlled in a mannersuch that the sequential operations of the wells are exactlysynchronized in a desired sequence which cannot vary even over a longperiod of time. This :is possible with the system according to thisinvention since it enables the use of `a single motor driven cam shaftlarrangement, whereby individual cams on such shaft may be set forproviding the desired sequence of the wells individual gas lift cycles.The sequence cannot vary, once it has been set, by reason of themechanical relationship of 4the cams to a -single shaft `or commondirect drive for all of them. Although a synchronized system has beensuggested before, it made use of electric controls that necessitatedcircuits connecting each well to a single point `and required use ofelectric power which is loften not available at a iield where gas liftpumping is being carried out.

Thus, it is an object of this invention to provide a superior gas liftcontrol `system which gives synchronization of intermittent ilow cyclesfor al1 of the wells in a given field.

Another object of this invention is to provide a gas lift control systemwherein the individual well gas lift timers are pneumatically poweredand thus need no periodic attention, e.g. winding of a spring motor, orthe like.

Another object of this invention is to provide a gas lift control systemwhich has a central control member that may be employed to shut down theentire iield simultaneously in case of some emergency.

Another object of this invention is to provide an irnprovernent for agas lift control system ywhereby the sole link connecting a centralcontroller with the individual well of the field, is the product ilowline from each well to the tank battery or central collection point.With this arrangement there is provided automatically, a means wherebyany well which develops a break in the ilow line therefrom becomesdeactivated and will not continue its ICC gas lift pumping cycles, solong as the .break in the ilow line remains.

Briey, the invention concerns a gas lift control system. The systemcomprises in combination, means for receiving pneumatic iluid underpresure from a source of pneumatic pressure, and means for receiving gasunder pressure from a source of high pressure gas. The system alsocomprises a central controller for providing pneumatic control signals,a plurality of wells each having a timer associated therewith, and atank battery having llow lines thereto from each of said wells. Inaddition, the system comprises means for applying said pneumatic signalsto each of said llow lines in sequence, and it comprises pressureresponsive means connected to each of said ilow lines adjacent to eachof said timers. `Finally, the system also comprises means actuated bysaid pressure responsive means for initiating :a cycle by e-ach saidtimer. The said timer cycle actuating means acts to control introductionof said high presure gas through t-he well associated with said timer.

Again briefly, the invention concerns a gas lift control system having aplurality of wells each having a timer for controlling application ofgas lift pressure thereto. The system is one wherein each of said wellshas a production ilow line from said well to a tank battery and whereinthe system has a central controller for actuating said timers insequence. In the foregoing control system the improvement comprisesmeans vfor transmitting actuating signals from said control to saidtimers, wherein the sole link connecting each of said wells with saidcentral controller is the production ilow line from said well t-o thetank battery.

The foregoing and other objects and benefits of the invention will beset forth more fully below in connection with the drawing wherein thefigure of drawings provides a schematic showing of a gas lift controlsystem indicating one of a plurality of wells and the tank battery towhich the wells are connected.

Referring to the figure of drawings, it is pointed out that the singleligure includes a tank battery portion of the `whole schematic diagramand an individual well portion thereof. It is to be understood thatthere may be any number of individual Iwells making up the entire field,all of which are connected separately to allow the produced fluids fromeach to flow to a central location and be collected in the tank battery.The tank battery per se (not shown) includes as the input thereof aseparator 1i1 that has a product header pipe 12 which feeds theindividual ilows of produced iluid into the separator. As indicated inthe diagram, the output of separator 11 will be divided into itslconstituents `of. liquid (may be oil and water, or oil) and gas withboth being fed to the tank battery (not shown) for collection thereof.

It will be observed that there are a plurality of ilow lines 14 and 15connected into the product header pipe 12 (plus others depending uponthe number of wells) and each of these flow lines leads from a separatewell that is being produced by means of gas lift type fluid recovery.Control of each of these wells, insofar as initiation of a gas liftcycle is concerned, is carried out from a central location adjacent tothe tank battery. Thus for example, there is a llow line 15 that has acheck valve 16 therein (indicated schematically) close to the connectionof ilow line pipe 15 with the header pipe 12. Further back (up stream)along ilow line 15, there is a diaphragm actuated type valve 17 that isunder control of a pneumatic signal which is fed along a pneumatic line18 that is connected into another pneumatic line 19. Pneumatic line 19leads from one port of a three-way valve 22. Valve 22, in turn, ismechanically controlled by means of a cam 23 which is driven by a shaft,or other mechanical connection, 24 which in its turn is driven by amotor 25.

'It will be understood that motor 25 may take any feasible form, i.e.may be an electric motor or a pneumatic motor, etc. depending upon theconvenience of a source of power therefor. It is to be noted that themotor 25 (by means of an extension of the shaft or mechanical connection24) also drives another cam 28 that will be set at a different positionrelative to cam 23 so that another three-way valve 29 (corresponding tothree-way valve 22) will be actuated at a different time from valve 22and in an exactly controlled sequence, so as to maintain synchronous butstaggered operation of the valves 22 and 29 and all additional valvesfor the remaining wells in the eld.

There is a source of pneumatic pressure (not shown) which is connectedto an input pneumatic line 32 that leads to a pressure regulator 33 andthen via a pneumatic line 34 to a lease shutin valve 35. It will beobserved that the lease shutin valve 35 is schematically indicated asbeing a diaphragm actuated type. It is to be noted that although thereis no showing for the details thereof, there may be any desiredarrangement for controlling operation of shutin valve 35. This may be inconnection with maintenance of pneumatic pressure high level in tanks orthe like, so that under certain conditions (as may be predetermined) thevalve 35 will be closed and thus the entire lease or field will be shutin, and the gas lift pumping operations Will cease.

The pneumatic pressure supply as introduced from the pneumatic line 32via regulator 33 and shutin valve 35, is fed over a pneumatic supplyline 36 to inputs of all of the individual elements which together go tmake up the central controller for the field. As indicated above, eachof the plurality of well control units are all controlled by theoperation of motor 25 and the various cams, e.g. 23 and 28, operatedthereby.

Since all of the individual control signal units of the centralcontroller are substantially identical, only one need be described indetail. Thus, referring to the pneumatic pressure signal unit whichfeeds signals into the ow line via the illustrated elements (whichinclude as the primary control elements therefor the three-way valve 22operated by cam 23) there is a pneumatic line 39 leading from the supplyline 36 to a pressure regulator 40 for reducing the pressure from arelatively high figure, e.g. one hundred pounds per square inch, on thesupply line 36, down to a low pressure for use in actuating diaphragmcontrol elements of pressure controlled valves, e.g. twenty pounds persquare inch. Leading from the low pressure side of regulator 40 there isa pneumatic line 43 that is common to all of the control signal units.Consequently, in the unit being described (which supplies signals toflow line 15) there is a pneumatic line 44 that leads to an input port0f the three-way valve 22 mentioned above.

Valve 22 has in addition to the port connected to pneumatic line 19 andthe port connected to line 44, a port connected to an exhaust line 45,as indicated by the caption Exh. The operation of three-way valve 22 issuch that the cam 23 will cause the valve to be positioned either withthe line 19 port being connected alternatively with pressure line 44 orwith exhaust line 45. The pressure line 44 port (of valve 22) is closedwhenever it is not connected to the line 19 port.

It is to be observed that pneumatic line 19 connects to both pneumaticline 18 (leading to diaphragm actuator for the valve 17) and anotherpneumatic line 48 which leads to the diaphragm actuator of a valve 49.The valve 49 is connected in a pneumatic line 50 that leads directlyfrom the supply line 36 to the valve, and then through the valve 49 anda pneumatic line 51 to a check valve 52, that has the other side thereofconnected into the ow line 15.

The operation of each control unit is substantially identical, as waspointed out above, and will be readily understood by reference to thesteps involved in connection with the operation of the unit feeding flowline 15, the elements of which were described in detail above. Thus theoperation for creating a control signal pressure pulse, may be followedcommencing with the fact that pressure on supply line 36 is transferredto the input port (line 44) for three-way valve 22. This port is eitherclosed or opened for a short time, depending upon the position of cam 23that actuates the valve 22. Whenever the valve 22 is actuated to openthe port from the input line 44, pneumatic pressure is transferred viathe pneumatic line 19 to both lines 18 and 48 s0 that the diaphragmactuators of valves 17 and 49 respectively will receive pressure. Thesevalves (17 and 49) which are normally biased to the open and closedpositions respectively, will thus simultaneously be actuated so thatvalve 17 is closed while valve 49 is opened. This means that pneumaticpressure will be supplied over pneumatic line 50 through valve 49,pneumatic line 51 and via valve 52, into flow line 15. At the same timevalve 17 will be closed and so prevent escape of this pneumatic pressuresignal along ow line 15 toward the tank battery. Consequently pneumaticpressure will build up in flow line 15 back toward the well that isconnected thereto. Also, by reason of a check valve 55 in the ow line 15near the well, the pneumatic pressure will rapidly increase and thispressure increase will actuate a pressure sensitive element 56 that isassociated with a pneumatic timer 57 (captioned Pneumatic Intermitter)for controlling the gas lift operation at this Well.

Shortly after the foregoing action (which created a pressure signal) hastaken place, cam 23 will return three-way valve 22 to its yotherposition, such that pneumatic line 44 is cut off while the line 19 isconnected to the exhaust line 45. This will cause pressure to beexhausted from the diaphragm controllers of valves 17 and `49 so thatthey will return to their normal or biased position, which means thatvalve `17 wil-l 'be opened while valve `49 will be closed. Consequentlythe pressure signal that was applied to the flow line 15 will bedissipated by the Iopening of valve 17, and the flow line will be incondition to receive a flow of production fluid when the gas liftpressure is applied to the well.

It is to be noted that in lconnection with each Well there is apneumatic timer, eg. timer 57, which may .take any feasible form butpreferably is substantially like a timer described and claimed in acopending application Serial No. 216,836, led August 14, 1962, nowPatent No. 3,152,611, which acts by means of pneumatic and hydraulicelements to control the timing of a cyclic operation of valve openingland closing. It is this valve oper-ation that acts `as the control forapplying so-called power gas to the well for providing the gas liftforce.

While the details of a pneumatic timer like the pneumatic timer 57illustrated, are more fully set forth in the aforementioned copendingapplication, the elements of the timer 57 will be described heresuficiently to provide an understanding of the general operationthereof. In this connection it is pointed out that at the well there isa supply pipe `58 for introducing high pressure gas to the well toprovide the so-called gas lift pressure that drives the -productionfluid up through Well tubing 59 that is connected in turn to the flowline 15 via the check valve 55, already mentioned. The `operation of agas lift fluid recovery cycle in a well, is well known and merelyconsists of the periodic introduction of high pressure gas to theannulus of a well -that is closed top and bottom having tubing .thereinthat extends down hole with `a plurality of gas lift valves and relatedstructure `at the production fluid level. The gas pressure acts to forceaccumulated fluid from Within the tubing plus gas lift valve structure,up the tubing and out Vthrough the flow line connected to the Well.Application of the gas pressure is timed to lift the accumulatedquantity of duid and then is cut off lfor a suicien-t period to allow afurther accumulation of fluid down hole within the gas lift tubingstructure.

Control of the introduction of the high pressure gas for each lift cycleis carried out by means of a valve 62 that has a diaphragm, or othertype of pressure actuator 63 for opening the valve 62 when pressure isapplied to the actuator. The valve is biased to a closed position in theabsence of pressure on the actuator 63. The timer 57 controls theduration of the opening of valve 62 as wi-ll be described.

The elements of the timer 57 include .a pneumatic pressure line 66 thatleads from the power gas supply in pipe `58 `to a pressure regulator 67.On the other side of pressure regulator 67 there is a pneumatic line 6-8that connects to two pneumatic lines 69 and 70. Line 70 leads to aninput port of a three-way valve 73 which is either closed or connectedto a port leading to a pneumatic line 74 that is T connected to twoadditional pneumatic lines 75 and 76. The third port of three-way valve73 is open to exhaust and the three-way Valve itself is of a type whichwill act to connect the pneumatic line 74 alternatively with the inputport (leading to pneumatic line 70) or with the exhaust port that leadsto the atmosphere. Furthermore it is to Ibe observed that three-wayvalve 73 is a double-diaphragm actuated type so that there is adiaphragm actuator 78 for positioning the Valve to connect line 70 withline 74, and there is another diaphragm actuator 79 that will positionthe valve to its other state whereby pneumatic line 70 is closed whileline 74 is connected to exhaust through 4the other port of the valve 73.

`It will be observed that the pneumatic line 76 is connected to thediaphragm actuator 63 of power gas valve 62, while pneumatic line 75connects to the upper portion of one chamber 82 that is part of lthetiming mechanism for the timer unit 57. Chamber 82 contain-s a liquid,eg. hydraulic iluid 83, during part of a cycle and has connected to thelower portion of the chamber a pair of pneumatic lines each containing arestriction 86 and `87 respectively, for regulating the rate of llow ofthe hydraulic fluid `83 therethrough. Iln addition, there are checkvalves 88 and 89 respectively, each in series in the line which containsrestrictions 86 and 87 respectively, while both of these lines arejoined together to carry uid ow via a line 90 to the lower portion ofanother chamber 91. Chamber 91 has connected to the kupper portionthereof `a pneumatic line 92 that is connected directly to the diaphragmactuator 79 of the three-way valve 73.

In addition to the above described elements of the timing unit, there isassociated with the pressure responsive element 56 a three-way valve 95.that has connected to an input port thereof `a pneumatic line 96. Anoutput port of the valve 95 is connected to a different pneumatic line97 which leads directly to the diaphragm actuator 78 of .three-way valve73. The third port `of valve A95 is `left open for connecting line 97alternatively to exhaust, i.e. the atmosphere, when the three-way valve95 is in one of its .two positions; while the line 97 is connected tothe line 96 when valve 95 is in the other of its .two positions. On theother end Aof pneumatic line 96 there is a pressure regulator ,100 thathas connected to the other side thereof the pneumatic line 69, which asindicated above leads via line 68 to the low pressure side of regulator67.

The timing unit 57 acts, as indicated previously, to open the valve 62for a predetermined relatively short time `and then close same oncemore. This acts so that the high pressure gas lift is introduced intothe well for `a sufficient period of time to insure the completeejection `of all lof the produced uid from the well, which hasaccumulated since the previous application of `such pressure. Theoperation of the timing unit which determines this period of valveopening time, -may be briefly reviewed here while the full detailsthereof will be more fully appreciated in connection with the disclosureof .the aforementioned copending Iapplication. It is to be noted,however, that in the present application (of .a pneumatic timeraccording to the copending application) there is an arrangement forinitiating a timing cycle upon receipt of -a pressure signal that istransmitted from a central controller location along the flow line thatconnects the well to the tank batte-ry where product is gathered.

Thus, a timing cycle (as initiated by receipt of a control signal) maybe described with reference to the timing unit illustrated, in thefollowing manner. When a pressure increase is received within ow line 15(between check valve 55 and the closed valve 17) by reason of the actionat the central controller which causes such pressure rise, the pressureresponsive element 56 will cause actuation of the three-way valve so asto connect pneumatic pressure from line 96 to line 97 which leads todiaphragm actuator 78. Diaphragm actuator 78 will then cause three-wayvalve 73 to be shifted so that it connects the input pressure line 70with output line 74 that leads to both the diaphragm 63 of gas liftvalve 62 and the upper portion of chamber 82 (which at that time willcontain hydraulic uid 83 therein). Consequently valve 62 will be openedto supply power gas to the well, and a timing cycle will be commenced todetermine the length of time that this valve is to be held open.

This timing cycle (which may be set as desired) is determined by the owof hydraulic `iluid from chamber 82 into chamber 91 followed by asufficient increase in pneumatic pressure at the output (pneumatic) sideof chamber 91 so as to actuate the three-way valve 73 back to its otherposition. The latter action takes place by means of the pressureintroduced into diaphragm actuator 79. The length of time involved inthis action is preset by means of the amount of liquid 83 and by thesize of restriction 86 which may be variable and could take the form ofa needle valve for example. The ow of uid 83 is confined to the passagethrough restriction 86 and not that containing restriction 87, by reasonof the orientation of check valves 88 and 89. The orientation of thesecheck valves is such that flow is permitted only in the indicateddirections, i.e. flow through restriction 86 takes place when fluid isowing from chamber 82 to chamber 91 while the reverse is true when fluidis flowing back from chamber 91 to chamber 83 (when it passes onlythrough restriction 87).

It will be observed that while tluid 83 is iiowing from chamber 82 intochamber 91, the transfer is relatively slow and the compression of thegas on pneumatic uid in chamber 91 is relatively slight, so that noactuation takes place of three-way valve 73 due to actuator 79 thereof.However, when fluid 83 has all passed out of chamber 82 and gone throughrestriction 86, the passage of pneumatic iluid is much more rapid (dueto the difference in viscosity) and a sudden increase in the flow and inthe pressure caused to pneumatic uid in chamber 91, will take place.This pressure increase will be sufficient to actuate pressure actuator79 and shift valve 73 back to the original state thereof, since in themeantime three-Way valve 95 will have returned to its non-pressureposition due to the reduction in pressure of the pressure signal withinflow line 15. Consequently, the three-way valve 95 is positioned toconnect diaphragm actuator 78 (via pneumatic line 97) with exhaust,while pneumatic line 96 is cut off.

When three-way valve 73 is thus shifted by action of actuator 79, theinput pneumatic line 70 is cut off while output line 74 is connected toexhaust. Consequently the pressure on diaphragm actuator 63 of the gaslift valve 62 will be exhausted and simultaneously pneumatic pressure onthe upper portion of chamber 82 will be also connected to exhaust. Thisthen will set up conditions so as to commence a return of the hydrauliciluid 83 from chamber 91 back into chamber 82 via restriction 87, whichin the present use of the timer will be set relatively wide open topermit quick return of the liquid. At this time (following return of theliquid 83) the timer unit will stand at rest awaiting the next pressuresignal from within flow line 1S to commence another similar timing ccle.

yIt is to be understood that none of the specific elements involved inthe system according to this invention contribute per se, as elements ofthe invention. In other words, it is pointed out that in case ofthree-Way valves such as valves 22, 29, 73 and 95 which areschematically illustrated, any commercial valve structure that isavailable and designed to accomplish the indicated results may beemployed in the system. In this connection it may be reiterated that inthe case of valves 22 and 29 (and all additional like valves in thesystem) the valve structure is one that may be operated mechanicallyfrom a central control structure such as a shaft, with cam elements forshifting the valve from one position to the other at a predeterminedrotational position of the shaft. Similarly valve 73 is a three-wayvalve that has a pair of diaphragm actuators therefor and is not biasedto either of its two operating positions. The operation is such thatwhen pneumatic pressure is applied to either one of the diaphragmactuators the valve will be shifted to a given position as caused bythat actuator. Then the valve remains in such position until pneumaticpressure is applied to the other diaphragm actuator which will shift thevalve to its opposite state or position where it will remain untilshifted back by the other actuator. Likewise valve 95 is a three-wayvalve that may be shifted from one position to which it is biased (by aspring or the like) to the other position upon receipt of pressure inthe pressure sensitive control element 56. It will be appreciated byanyone skilled in the art that the element 56 may take various forms,eg., a diaphragm or a bellows type structure. The mechanical connectionfrom element 56 to the valve 95 is schematically indicated by the dashedline shown. When such pressure is removed or falls below a given levelthe valve will be shifted back to the spring biased position thereof.All of the foregoing valves as well as the various other single-typevalve structures illustrated, are commercially available on the openmarket and may be purchased for use as specified to meet the conditionsrequired. Thus, as indicated above there is no invention in thestructural details of any of the valves or similar elements in thesystem shown, per se. Rather, the invention lies in apneumatic-hydraulic control system that is applicable to a gas liftoperation.

It is to be observed that among the advantages of this invention is thefact that, in addition to providing a central control signal arrangementfor an entire gas lift field, any break in an individual one of the fiowline connections from each well to the tank battery will automaticallycause a shutdown of the well that has such a broken flow line, since thepressure signal will never be able to build up within such flow line toinitiate a timing cycle for introducing gas lift pressure to that well.

While a particular embodiment of the invention has been described inconsiderable detail in accordance with the applicable statutes, this isnot to be taken as in any way limiting the inventign but merely as beingdescriptive thereof.

I claim:

1. A gas lift control system for a plurality of wells comprising incombination, first conduit means for receiving and transmittingpneumatic fluid under pressure from a source of pneumatic pressure,second conduit means for receiving and transmitting gas under pressurefrom a source of high pressure gas to the wells of said system, acentral controller for providing pneumatic control signals in the formof pressure pulses and having said first conduit means connectedthereto, a plurality of wells each having a cyclically operable timerassociated therewith to control the duration of application of said highpressure gas to said well, a tank battery having flow lines thereto fromeach of said wells, means for applying said pneumatic signals from saidcentral controller to each of said ow lines in sequence, pressureresponsive means adjacent to each of said wells and being connected toeach of said flow lines adjacent to each of said timers, and meansactuated by said pressure responsive means for initiating a cycle by thecorresponding one of said timers.

2. The invention according to claim 1 wherein said timers are pneumatic.

3. The invention according to claim 2 wherein said pneumatic signalscomprise a pressure increase sufficient in duration to cause a rise inpressure at said pressure responsive means, and said signal applyingmeans comprises a concurrently actuated valve in each said ow linelocated between said tank battery and a pneumatic line connecting eachpressure responsive means with the corresponding ow line.

4. The invention according to claim 3 wherein said central controllercomprises a motor, a plurality of cam actuated pneumatic valves forintroducing said pneumatic signals from said first conduit means to saidflow lines, and cam means driven by said motor for sequentiallyactuating said valves.

5. The invention according to claim 4 further including a centralshut-in valve associated with said first conduit means for cutting offsaid source.

6. In a gas lift control system having a plurality of wells each havinga timer for controlling application of gas lift pressure thereto, eachof said wells having a production flow line from said well to a tankbattery, and a centrally located controller for actuating said timers insequence, the improvement comprising means for transmitting pneumaticpressure signals from said controller to each of said timers solelythrough each said production ow line from said well to the tank battery.

References Cited by the Examiner UNITED STATES PATENTS 2,736,201 2/56Ohlsen et al. 166--52 X 2,845,125 7/58 Truman l66-52 3,045,750 7/62Peters 166-52 3,070,033 12/62 Welchon 103-232 CHARLES E. OCONNELL,Primary Examiner.

1. A GAS LIFT CONTROL SYSTEM FOR A PLUARLITY OF WELLS COMPRISING INCOMBINATION, FIRST CONDUCIT MEANS FOR RECEIVING AND TRANSMITTINGPNEUMATIC FLUID UNDER PRESSURE FROM A SOURCE OF PNEUMATIC PRESSURE,SECOND CONDUIT MEANS FOR RECEIVING AND TRANSMITTING GAS UNDER PRESSUREFROM A SOURCE OF HIGH PRESSURE GAS TO THE WELLS OF SAID SYSTEM, ACENTRAL CONTROLLER FOR PROVIDING PNEUMATIC CONTROL SIGNALS IN THE FORMOF PRESSURE PULSES AND HAVING SAID FIRST CONDUIT MEANS CONNECTEDTHERETO, A PLURALITY OF WELLS EACH HAVING A CYCLICALLY OPERABLE TIMERASSOCIATED THEREWITH TO CONTROL THE DURATION OF APPLICATION OF SAID HIGHPRESSE GAS TO SAID WELL, A TAN BATTERY HAVING FLOW LINES THERETO FROMEACH OF SAID WELLS, MEANS FOR APPLYING SAID PNEUMATIC SIGNALS FROM SAIDCENTRAL CONTROLLER TO EACH OF SAID FLOW IN SEQUENCE, PRESSURE RESPONSIVEMEANS ADJACENT TO EACH OF SAID WELLS AND BEING CONNECTED TO EACH OF SAIDFLOW LINES ADJACENT TO EACH OF SAID TIMERS, AND MEANS ACTUATED BY SAIDPRESSURE RESPONSIVE MEANS FOR INITIATING A CYCLE BY THE CORRESPONDINGONE OF SAID TIMERS.